There has already been a question about why Doc built the time train. My question is how he did it.

Doc clearly could not fix the DeLorean to return back to the future. Thus, he hid the car in the Delgado mine leaving Marty a letter which indicated that the necessary components would not have been invented until 1947.

And yet he somehow managed to build a time machine inside a train after he left with Clara in 1885. We know that the time train was already working when both his sons were not older than 10 years old. This means that he had build the time train presumably not later than 1895. Even at that time there were no electronic components available. How did he create the flux capacitor then?

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    I doubt there is an official answer to this question, and think we're meant to assume that at some point after Marty's departure, Doc thought of a simpler design that he could execute with the systems available to him. Either that or he figures out how to build the missing components (transistors?) in 1895. Commented May 28, 2017 at 10:48
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    Well, I would think since there was a problem with the car under the time machine the big problem was more like repairing a car without the spare parts. And he had no fuel either. So he took the saver aproach of hiding the car and not trying to smuggle it. This was also to help his friend. If he destroyed more Marty would have been stuck in 1955. I would assume the flux capacitor was not really that complex to build. And he learned new stuff in the future, too, so why not a less complex way to create electronics?
    – Daarin
    Commented May 28, 2017 at 12:08
  • I felt that my answer to this one was about as comprehensive as you're going to get unless they do a new film. Is there anything else you'd want me to address before considering an acceptance?
    – Valorum
    Commented Sep 22, 2017 at 11:50
  • My interpretation of the end scene where the Doc exclaims "It runs on steam!" was meant to signify both that Doc used a steam engine to get up to 88mph, as well as figuring out a way to use steam to generate 1.21 gigawatts without more advanced technology. But that's just a simple interpretation, the comics answer is definitely more comprehensive.
    – Tronman
    Commented Jan 28, 2018 at 13:08
  • I'd assumed that Doc received the necessary components and materials from a future version of himself, and once he had created the working time machine from a steam engine he went to the future, obtained the materials, and delivered them to his earlier self. Commented Apr 21, 2018 at 17:32

3 Answers 3


The very short answer is that (at least according to the IDW comics released by Bob Gale, the writer of the films) Doc Brown was able to cobble together a working time machine by using components from the hoverboard as well as his own knowledge of metallurgy and science.

comic panels with Doc describing how he used a frictionless dynamo
Back to the Future: #08

Although his time travel device (a modified steam car) was only able to make a single trip before breaking, he was able to travel forward into the 1980s to collect the items needed to return to the past and get the Jules Verne time-train working, then finally traveling to the 2050s to get it hover-converted before returning (after a few adventures) to give the picture to Marty.

Doc promises adventure

As to Flux Capacitor itself, building a simple capacitance chamber in the 1800s would be child's play for someone with a working understanding of chemistry, electronics and metalworking.


He also could use all the functional parts of the DeLorean hidden at the Delgado Mine (at the time of the film, there were TWO time machines at the place: the one in the mine to be discovered at the 50's, and the other that Marty used to get to that past and without oil).

The main problem at 19ht century was the lack of fuel, but Doc saw that rail locomotives were able to reach the limit speed. He could dismantle the flux capacitator, the time circuits, the Mr. Fussion device... Install all of them in a normal locomotive, travel to the future year 2050, adapt it to the Jules Train configuration, go back to the 19th century to return the "borrowed" original special parts of the DeLorean at Delgado Mine (for maintaining time continuity so Marty and young Doc could find it in the 50's), and then go back yo the future (the 80's) to meet Marty after the train crash.

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    This has been addressed. The Doc didn't use the Delgado Mine DeLorean; scifi.stackexchange.com/questions/50533/…
    – Valorum
    Commented Apr 20, 2018 at 22:40
  • Thanks, i haven't read that. Doc doesn't like the risk of a time paradox, so he'ld avoid to borrow parts from Delgado Mine... Except he'd thought "what the hell...?" as when reading the letters :-D Commented Apr 21, 2018 at 15:41

And remember when marty went back in time twice to meet the younger doc brown who got more knowledgeable about his own time machine. ...he kept making him self smarter about it...

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    Commented Jan 28, 2018 at 5:09

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